The present invention relates to the alignment of mating form tools, and more particularly to the alignment of a punch and lead form anvil to form the outer leads of an integrated circuit (I.C.) chip mounted on a tape automated bonding (TAB) tape.
The use of alignment pins for excising an I.C. chip and its extending outer leads from a tape segment and then forming the outer leads in a single operation so that the chip and its leads are ready to be bonded on a substrate or to be packaged is well known in the art. For instance, U.S. Pat. No. 4,064,917 to Diaz discloses a punch and I.C. chip mount on a punch press. The punch has cutting edges which press in conjunction with the die mount's cutting edges to severe the chip and its outer leads from a lead frame. The punch also has forming edges which press in conjunction with the forming edges of a die form block to bend the outer leads to a desired configuration. Additionally, alignment pins are provided which engage sprocket holes of a film segment in order to accurately position the film segment, the lead frame attached to the film segment, and a chip bonded to the inner portion of the frame relative to the die mount and die form block. Nevertheless, the use of pins that engage sprocket holes in the tape fails to provide alignment between the punch and die form block (i.e. lead form anvil). What is needed is a direct mechanical alignment link between the punch and lead form anvil. The solution to aligning the punch and lead form anvil is not as simple as engaging alignment pins through holes due to severe space limitations. Such alignment pins may need to fit inside a window closely shaped to the perimeter of the punch without lying directly beneath the chip or its outer leads. Generally the only available space would be in the corners between outer leads on adjacent sides of the chips. A punch wall thickness from cutting edge to forming edge of, for example, 0.030 inches, would require pins with such small diameters that the pins would probably be subject to bending, breakage, or other reliability problems. The space limitation problem is further compounded by the increasing miniaturization of TAB microelectronic components.
The prior art has the shortcoming that in order to align the excise and lead form tooling, it is necessary to perform the alignment manually by trial and error. A typical manual alignment procedure is performed by first loosely fitting the lead form anvil mounting screws, aligning the lead form anvil with the punch by hand, and tightening the screws. An experimental component is then lead formed and examined under a microscope. Invariably the leads will be improperly bent due to a slight misalignment between the punch and lead form anvil. It then becomes necessary to loosen the lead form anvil mounting screws and try again. This method of adjustment tends to be an unsystematic trial and error procedure, and a skilled technician will usually require at least 8 hours and often about 30 hours to properly complete the alignment since there is no direct mechanical link between the punch and the lead form anvil. Furthermore, it is often critical to maintain alignment during usage. Since all of the alignment devices are floating relative to the punch and lead form anvil, this allows a large tolerance stack up to occur. Misalignment becomes acute during TAB tape manufacturing due to the fact that very small inaccuracies, for example 0.001 inches, can cause unacceptable lead forms. Furthermore, as it becomes necessary to replace the punch or lead form anvil to comply with components having different dimensional specifications, the trial and error alignment procedure will once again be necessary.
From the foregoing several things can be understood by those persons skilled in the art. First, it is clear that punch and lead form anvil alignment is a difficult and time consuming process that must be performed during set-up as well as maintained during usage. Second, the prior art has failed to disclose or suggest a simple and convenient solution to this alignment problem.